For commercial users of LT, you could suggest a minimum donation (monthly or yearly) for each user in an organization.

For developers of products that use LT, you could suggest a minimum donation for each sale (possibly as a percentage of the sale value).

(Page https://languagetool.org/donate/ shows expenses as 50 euros. The correct value is more than 600 euros. I suggest that you also add a list of things that you would like to do, but which will cost money.)

Grammarly charges an arm-and-a-leg for the same product. In fact, your product is indistinguishable from theirs. Seriously, has anyone noticed this? Although I paid for a year's worth of Grammarly, I plan to switch over to LT. I think if you're running low on funds you need to offer a pro version for a fee. Just be cheaper than Grammarly!